Long-term effects of dieting


Around and around we go…

Eat less; exercise more. I’ve said it myself, in print (sorry about that, guys). This weight-loss advice isn’t wrong exactly, but it’s terribly incomplete. The causes of obesity are complex, and a sudden worldwide epidemic of people lacking willpower is definitely not the answer.

When people go on a diet, they usually lose weight. And then, with the same predictability, over the next few years the vast majority of dieters gain it back. Most of us blame ourselves, without appreciating the powerful biology that underlies the process. Substantial weight loss increases hunger and reduces metabolism – meaning that a successful dieter must eat less (forever) than someone of the same weight who’s always been thin.

The data on long-term outcomes of dieting that I presented in my TEDGlobal talk come from this review article. On average, five years after a diet, most people were back to their original weight. A substantial minority, 41% of dieters, regained more weight than they had lost. And yes, those statistics probably apply to your favorite diet, whatever it is. None of the ones that have been studied have fared better than others in the long term.

In reality, the long-term outcomes are probably worse than that, because such studies are hard to do well. On average, researchers only managed to get follow-up data for a third of the participants after five years. As you might imagine, people who’ve kept the weight off are more likely to respond to such requests than people who’ve gained it all back and then added more pounds. Many studies asked participants to report their own height and weight, which most people underestimate. Finally, researchers often don’t take into account whether participants have been on other diets since the study began. Repeated dieting (weight cycling) can resemble successful weight-loss maintenance if you don’t look too closely.

Losing weight isn’t the hard part. Fighting your brain’s persistent attempts to make you gain it back is a much bigger challenge. And the costs of failure can be high. I’ll have more on that aspect tomorrow.

Weight and health – show me the data!

Since I gave my talk on dieting at TEDGlobal, a few people have asked for the references. I like that spirit, so here you go. Today’s post is on weight and health. Tomorrow I’ll cover the long-term consequences of dieting, and Friday I’ll explain what happens to teenage girls who worry too much about their weight.

80614206 (1)My bar graph contained data from Figure 1 of this paper, showing that mortality is better correlated with healthy lifestyle habits than with weight. Researchers have a lot of evidence that fitness is a key to health, independent of fatness. As this commentary explains, obese people with moderate cardiovascular fitness (those who walk for 150 minutes a week, for example) are half as likely to die prematurely as normal-weight people who don’t exercise at all. A review article concluded that “active or fit women and men appeared to be protected against the hazards of overweight or obesity. This apparent protective effect was often stronger in obese individuals than in those of normal weight or who were overweight.” So if you’re obese, exercise is probably even more important to your health than it is for normal-weight or overweight people.

By the way, epidemiology suggests that the ‘normal’ weight range is set too low for optimum health. Most recently, this meta-analysis of many studies found that people in the ‘overweight’ range actually live a bit longer than people in the normal range. For more details on this research and the controversy surrounding it, check out this piece in Nature.

Of course I’m not suggesting that we should all go out and gain weight for our health. I am suggesting that focusing too much on weight loss distracts us from reliable – and easier – ways to promote health. No matter how much you weigh (and perhaps especially if you’re obese), eating a healthy diet and exercising 30 minutes a day are likely to extend your life.

Tuesday travel photography: light and loneliness

Rost, NorwayNorway has some of the best light on the planet. I took this photo on Rost, the outermost of the Lofoten Islands, on August 28, 2005. After a rough ferry ride from the mainland, we had to stay several days before the next ferry would allow us to depart. A storm had come through in the afternoon and ripped one of our host’s boats from the dock. He was in his eighties and too arthritic to run an outboard, so his wife called on my husband to retrieve the lost boat before it was swept out to sea. The next day she expressed her gratitude by fixing us a dinner of breaded cod’s tongues, a local delicacy.

Two days later an innkeeper on another island told us how sorry he was that New Orleans had been destroyed. We had no idea what he was talking about because we’d been completely out of touch with the world.

Mommybites radio show

If anyone who listened to me talk about self-control with Heather Ouida today didn’t get enough information, I wrote a series of posts for Big Think on the same topic recently. They include links to the research that I discussed, as well as a bonus video of me talking about how to praise children effectively.

And if you don’t have enough cute in your life, check out this video of kids taking the marshmallow test.

Tinkering under the hood – Being Human 2012

When I ask neuroscientists to estimate how much we understand of how the brain works, the answers usually range from two to five percent. So I wasn’t surprised that one recurring theme at the Being Human meeting in San Francisco on Saturday was what researchers don’t know about the brain.

This ignorance extends to our own brains. Many of the speakers emphasized what a small fraction of the brain’s activity filters through to conscious awareness. As David Eagleman put it, “The conscious part of you is the smallest part, like a broom closet in a mansion.” Basic functions, like seeing color, feel easy introspectively because they rely on complex assumptions that don’t reach awareness. Knowing about these assumptions doesn’t change our perceptions, but it can challenge the intuitive idea that we perceive reality itself instead of abstract representations of reality. (Of course, that doesn’t mean that reality is all in your head. Sorry, New Agers and Matrix fans.)

Although the thought of not knowing what’s going on in your own mind may be disconcerting, the vast extent of subconscious processing is a feature, not a bug. Attention is a limited resource, so it makes sense to apply it only where it’s helpful. Besides, as several speakers mentioned, a lot of brain functions are too important to be left to our unreliable conscious minds. What if you got caught up in a novel and forgot to breathe? Given the irrepressible human desire to tinker and try to improve things, we could cause considerable mischief if it became possible to get under the hood of our brains and mess around.

Another area where introspection misleads us is the sense of having a unified self. It sounds pompous to refer to yourself in the plural, but the royal “we” may be a more accurate description of an individual than “I,” as Paul Bloom explained beautifully in The Atlantic a few years ago. The notion of arguing with yourself seems to be more than a metaphor.

The influence of culture on the brain is something I’d like to see more neuroscientists studying. Psychologist Hazel Markus spoke about the broad differences between independent and interdependent cultures. The U.S. middle class is an example of the former, in which people think of themselves as individual, unique, influencing others, free, and equal. The working class, in contrast, is an interdependent culture, in which people feel relational, similar, adjusting to others, rooted, and ranked. It occurs to me that a lot of the culture war between liberals and conservatives can be explained by those value differences.

Worldwide, independent cultures are vastly outnumbered by interdependent cultures, but among research subjects the reverse is true. Indeed, almost all neuroscience and psychology has been done on so-called WEIRD people, an acronym for Western, educated, industrial, rich, and democratic—largely on that most convenient of samples, college sophomores. Beau Lotto pointed out that people from different cultures even experience perceptual illusions differently, suggesting that a lot of what we know about the brain may have limited applicability to most of the world’s population.

The last session focused on meditation and other contemplative practices. Overall, the approach to that topic was refreshingly free of woo, though like Jason Goldman (read his meeting report), I got tired of hearing about all the times that speakers had met His Holiness The Dalai Lama. At the end, Richie Davidson returned to the theme of ignorance, saying that honest scientists must relish uncertainty and approach the brain with humility…which is also good advice for science writers.

Running from Alzheimer’s disease

Seniors_Walking_The_Beach_4146426The last time Sam Wang and I wrote about the value of exercise for the aging brain, we got a comment that made us laugh out loud. A video gamer dismissed us as “jocks” who didn’t understand the lifestyles of nerds. To the contrary, we’re both nerds in good standing who have never been described as jocks by anyone who’d met us. I don’t like to exercise all that much, but I keep encouraging everyone to do it anyway. And I take my own advice.

The reason that I do is because those of us who exercise have better brain function than sedentary people from preschool through old age. Exercising regularly from middle age reduces the risk of developing Alzheimer’s disease in your 70s by a factor of three. Starting to exercise as late as your 60s can still reduce the risk by as much as half. Now a new study reports that exercise reduces the buildup of an Alzheimer’s disease-associated protein called amyloid in the brain, particularly in people with a genetic susceptibility to the disease.

Among the genes identified as risk or protective factors, one has a stronger effect than all the rest put together. People with two copies of the risky allele of the ApoE gene, ApoE4, get Alzheimer’s fifteen years earlier than people with the protective allele, on average. The risky allele also speeds the cognitive decline associated with ordinary aging. Even cognitively normal people with the ApoE4 allele have more amyloid in their brains than people without the allele, as shown by PET imaging with a radioactive tracer. In long-term studies, people with a lot of amyloid revealed by this type of imaging are more likely to develop Alzheimer’s later on.

Previous studies have suggested that exercise has extra cognitive benefits for people with the ApoE4 genotype, and the new study provides a clue to why that might happen. Participants who met the American Heart Association recommendation of 30 minutes of moderate exercise on five days per week were considered to be exercisers, while people who did less (many did nothing) were categorized as sedentary.

downloadAs expected, people with at least one copy of ApoE4 had more brain amyloid than people without the allele, and exercisers had less amyloid than non-exercisers. The effects of exercise on amyloid were especially strong for people with the ApoE4 genotype, suggesting that they are particularly vulnerable to the bad effects of a sedentary lifestyle on the brain. As the figure shows, people with ApoE4 who exercised had less brain amyloid than people without the risky allele who were sedentary. This study shows that regular exercise eliminates the excess risk of brain amyloid accumulation associated with the ApoE4 genotype — and suggests that it may greatly reduce the risk of Alzheimer’s disease in people with this genetic susceptibility.

There’s one important caveat to the exercise recommendation: people with the ApoE4 gene variant have an increased risk of brain damage following head injury, so they should avoid playing contact sports. A disease called chronic traumatic encephalopathy or CTE has symptoms resembling those of Alzheimer’s disease, Parkinson’s disease, or Lou Gehrig’s disease. (Researchers now suspect that the famous baseball player had CTE, misdiagnosed as the disease that was named after him.) Professional soccer players in Italy are more likely to be diagnosed with Lou Gehrig’s disease than the general population. Professional football players in the US have a higher than average incidence of depression and memory problems, which may be due to CTE, as reported in an extensive series in The New York Times(Teenagers have a particularly high risk of brain damage from contact sports.)

Given these concerns, those of us who manage to exercise despite our lack of enthusiasm might be better off than the real jocks in some ways. But there’s no question that both groups can look forward to a sharper old age than most sedentary people.

Social skills and achievement

When I was in first grade, I convinced my teacher that it would be a good idea for me to work on advanced math problems during recess. To me, that seemed like an inspired solution to my social difficulties. An intensely shy girl, I was intimidated by the idea of having to find my way into a group of children, and I already knew that I could reliably distract adults from my shortcomings by flashing my intellect.

Luckily for my future, my mother didn’t fall for it. When the teacher asked for permission to implement my scheme, my mother wrote back: “Sandra doesn’t need to practice math. Sandra needs to practice recess. Make her go outside and play with the other kids.”

Mom was more right than she knew. Research shows that teaching interpersonal skills enhances academic achievement, even when it takes time away from subject-matter instruction. School-based programs to promote social skills have a strong track record of boosting test scores.

A recent meta-analysis evaluated 213 studies of social and emotional learning programs in over 270,000 students. These programs are designed to promote self-awareness, self-control, social awareness, relationship skills, and responsible decision making. About three-quarters of the programs lasted less than a year, and the remainder one or two years.

On average, the programs improved students’ social skills substantially. To a lesser extent, they also improved attitudes and social behavior, while reducing misbehavior and signs of emotional distress, such as depression or anxiety. About half the studies measured academic achievement, finding an average increase in test scores of 11 percentile points—meaning that a child who was initially ranked 13th in a class of 25 would move up to 10th after the program. Indeed, social skills instruction improves test scores as much as typical targeted academic interventions.

Programs taught by teachers in the regular classroom were as effective as the programs taught by outside experts. The more effective programs built up skills in a series of steps, used active learning strategies (such as coaching and role playing), focused on social skills specifically, and targeted those skills explicitly.

From a neuroscience perspective, these programs probably work by strengthening the frontal cortex. Various parts of this late-developing brain area are responsible for planning and organizing behavior and for monitoring and managing emotions. All those skills contribute to effective learning.

The best news for parents is that the effects of improved social skills and self-control can last a lifetime. Childhood self-control predicts success not only in academics, but also in work, marriage, and friendship. My mother may not have known all the details, but her instincts were right on target that social development is as important as intellectual development to life success.

Why you want your teen to talk back

For years I’ve been telling the exasperated fathers of mouthy teenage girls to relax. When she starts dating, I say, the ability to stand up to men will turn out to be a feature, not a bug — so you don’t want to discourage it too much.

new paper in the journal Child Development backs up my logic by demonstrating that teenagers who argue with their mothers are more likely to resist peer pressure to use drugs and alcohol. Almost all adolescents have friends who are doing something that their parents wouldn’t like if they knew about it, so parents are right to worry about the negative influences of peers. But not all teens are susceptible to bad influences. Indeed, some of them end up helping to straighten out their misbehaving friends.

What factors determine which teen is the influencer and which is the influenced partner in a friendship? Researchers showed earlier that teens whose parents are overly restrictive are more likely to be influenced by their peers. This type of research, though, is complicated by the fact that kids choose their friends, in part because they are similar to start with. Overbearing parents may produce rebellion in their teens, which then leads them to pick equally rebellious friends and copy their behavior.

To get around this problem, the authors of the new study tracked changes in the behavior of an economically diverse group of teens over several years. At age 13, the subjects were asked to talk with their mothers about an area of disagreement, and then at 15 and 16, their drug use was evaluated. Teens who had rapidly reversed their position when arguing with their mothers were substantially more likely to use drugs and alcohol later on, but only if their friends were users. Other factors that increased peer influence were low support from mothers, highly popular friends, and weak teen social skills.

So the next time your teenager is giving you lip, take a deep breath and remember that learning to say no effectively is an important social skill in its own right.